Field of the Invention
The present invention relates to an infrared-reflective film (heat reflective film).
Description of the Related Art
An infrared-reflective film is adhered to a building window, a vehicle window so as to be used to improve cooling or heating effect. Further, an infrared-reflective film is adhered to a window of a refrigerated (freezing) counter display to be also used to improve cold reserving effect.
FIG. 5 is a cross-sectional view of a conventional infrared-reflective film 70. In the conventional infrared-reflective film 70, an infrared-reflective layer 72 is formed on one surface of a substrate film 71 (transparent polymer film). The substrate film 71 is to be used as a base of lamination and a polyethylene terephthalate film is preferably used as the substrate film 71.
The infrared-reflective layer 72 is a laminated layer in which a metal thin layer is interposed between transparent dielectric layers respectively having a high reflective index. The infrared-reflective layer 72 transmits visible light, however, reflects infrared-reflective beams. The infrared-reflective layer 72 is formed on the substrate film 71 by a sputtering method or the like.
Far-infrared rays included in irradiation light 73 from above the infrared-reflective layer 72 are reflected by the infrared-reflective layer 72. Far-infrared rays included in irradiation light 74 from below the substrate film 71 are, however, mostly absorbed in the substrate film 71 as mentioned below.
Since polyethylene terephthalate contains plenty of C═O groups, C—O groups, and aromatic groups, the polyethylene terephthalate exhibits vibration absorption of a far-infrared region of 5 μm to 25 μm. Accordingly, polyethylene terephthalate has a property of absorbing far-infrared rays.
In the infrared-reflective film 70 shown in FIG. 5, a polyethylene terephthalate film is used as the substrate film 71. Accordingly, the substrate film 71 absorbs a part of far-infrared rays included in the irradiation light 74 from below the substrate film 71 to increase the temperature.
The temperature further increases because the substrate film 71 absorbs a part of far-infrared rays included in reflective light emitted to the lower side of the infrared-reflective layer 72. As a result, the irradiation light 74 from below the substrate film 71 is mostly absorbed in the substrate film 71. The substrate film 71 itself thereby re-emits infrared rays.
While the infrared-reflective film 70 shown in FIG. 5 reflects far-infrared rays when the irradiation light 73 comes from an infrared-reflective layer 72 side (upper side), the infrared-reflective film 70 does not reflect far-infrared rays when the irradiation light 74 comes from a substrate film 71 side (lower side). Accordingly, the infrared-reflective film 70 shown in FIG. 5 does not have enough infrared-reflective properties.
FIG. 6 is a cross-sectional view of another conventional infrared-reflective film 80 (Japanese Unexamined Patent Application Publication No. 2011-104887 A). In the infrared-reflective film 80 shown in FIG. 6, an infrared-reflective layer 82 and a protective layer 83 are formed on one surface of a substrate film 81. The substrate film 81 is a film to be a base of lamination and a polyethylene terephthalate film is preferably used as the substrate film 81.
The infrared-reflective layer 82 is a laminated layer in which a metal thin layer is interposed between transparent dielectric layers with a high refractive index. The infrared-reflective layer 82 transmits visible light. However, the infrared-reflective layer 82 reflects infrared-reflective rays. The infrared-reflective layer 82 is formed on the substrate film 81 by the sputtering method or the like.
In the infrared-reflective film 80 shown in FIG. 6, a polycycloolefin layer is used as a protective layer 83. Since the basic chemical constitution of polycycloolefin consists of carbon atom and hydrogen atom, polycycloolefin exhibits a little absorption of a far-infrared region. Accordingly, far-infrared rays included in irradiation light 84 from above the protection layer 83 reaches the infrared-reflective layer 82 without mostly being absorbed in the protective layer 83 to be reflected at the infrared-reflective layer 82. Far-infrared rays included in reflective light 85 reflected by the infrared-reflective layer 82 are also scarcely absorbed in the protective film 83 and are emitted outward. Accordingly, there is almost no increase in the temperature of the protective layer 83.
However, as mentioned below, far-infrared rays included in irradiation light 86 from below the substrate film 81 are mostly absorbed in the substrate film 81.
In the infrared-reflective film 80 shown in FIG. 6, a polyethylene terephthalate film is used as the substrate film 81. Accordingly, the temperature of the substrate film 81 rises by absorbing a portion of far-infrared rays included in irradiation light from below the substrate film 81. The temperature of the substrate film 81 further rises by absorbing a portion of far-infrared rays included in reflective light emitted to the lower side of the infrared-reflective layer 82. As a result, irradiation light 86 from below the substrate film 81 is mostly absorbed in the substrate film 81. This substrate film 81 itself thereby re-emits infrared rays.
While the infrared-reflective film 80 shown in FIG. 6 reflects far-infrared rays when the irradiation light 84 comes from a protective film layer 83 side (upper side), the infrared reflective film 80 does not reflect far-infrared rays when the irradiation light 86 comes from a substrate film 81 side (lower side). Consequently, the infrared-reflective film 80 shown in FIG. 6 does not have sufficient infrared-reflective properties.
FIG. 7 is a cross-sectional view showing still another conventional infrared-reflective film 90 (an infrared rays cut filter) (Japanese Unexamined Patent Application Publication No. 2006-30944 A). The infrared-reflective film 90 shown in FIG. 7 is a film in which infrared-reflective layers 92, 93 are formed on both surfaces of a substrate film 91 (a transparent resin film). The substrate film 91 is a film to be a base of lamination and a norbornene resin film or a polyether sulfonic resin film is used as the substrate film 91.
The infrared-reflective layers 92, 93 are both dielectric multi-layers, in which a dielectric layer A and a dielectric layer B with a refractive index higher than the dielectric layer A are alternately formed. Although the infrared-reflective layers 92, 93 allow visible light to transmit, the infrared-reflective layers 92, 93 reflect far-infrared rays. The infrared-reflective layers 92, 93 are formed on the substrate film 91 by the deposition evaporation method.
The infrared-reflective film 90 shown in FIG. 7 has the infrared-reflective layers 92, 93 on both surfaces thereof. Accordingly, regardless of a material of the substrate film 91, the infrared-reflective film 90 similarly reflects both far-infrared rays included in the irradiation light 94 emitted from the upper side and far-infrared rays included in the irradiation light 95 emitted from the lower side. Consequently, the infrared-reflective film 90 shown in FIG. 7 has superior infrared rays reflective properties.
However, it costs expensive to produce an infrared-reflective film 90 shown in FIG. 7 because the infrared-reflective layers 92, 93 have to be formed on both surfaces thereof.
Since the infrared-reflective film 90 shown in FIG. 7 has the infrared-reflective layers 92, 93 on both surfaces thereof, the infrared-reflective film 90 has a low transmittance of visible light. Accordingly, the room gets dark when the infrared-reflective film 90 is used for a window of a building. Further, when the infrared-reflective film 90 is adhered to a refrigerated (freezing) counter display, it becomes hard to see inside the refrigerated (freezing) counter display. Accordingly, the infrared-reflective film 90 shown in FIG. 7 has a drawback in practicability.